Fluid suspension spring and dampener for vehicle suspension system

ABSTRACT

A vibration isolating and damping suspension strut for vehicle undercarriages comprising an elongated cylinder and piston structure wherein the cylinder is divided into opposed chambers which are in communication with each other by passages formed in the piston and in a flow restricting shuttle valve mounted on the piston rod. When the strut undergoes a retraction stroke of the piston to absorb loads silicone fluid is compressed in the opposed chambers and transferred from the chamber opposite the piston rod to the rod side chamber through passages in the piston only. When the strut rebounds or extends its piston rod fluid is forced to flow through passages in the shuttle valve member and the piston flow passages at a more restricted rate. The piston flow passages and the shuttle valve are arranged to direct fluid flow toward the outer cylinder borewall to improve heat transfer to the exterior of the strut and minimize heating of the fluid contained in the cylinder chambers. Alternate embodiments of the suspension strut have spiral fluid transfer grooves formed on the periphery of the piston or on a cylinder sleeve insert member.

This is a continuation of application Ser. No. 753,365, filed July 5,1985, now abandoned, which is a continuation of application Ser. No.550,883, filed Nov. 9, 1983, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a combination telescoping piston andcylinder suspension spring strut and vibration dampener for vehiclesuspension systems.

2. Background

In the art of vehicle suspension systems there have been severaldevelopments directed to improving the isolation of the vehicle framefrom stresses and excursions of the vehicle resulting from uneven orrough roadway conditions and others factors inducing vibration in thevehicle undercarriage. Hydraulic, and/or combination pneumatic andhydraulic suspension mechanisms are desirable for several reasonsincluding improved fatigue life of the mechanism, improved vibrationdamping characteristics and the contribution of the mechanism toflexibility in the design of the vehicle undercarriage and frame.However, prior art hydraulic suspension spring and vibration dampenermechanisms have disadvantages which have presented certain problems tothe art worker.

One problem associated with known types of liquid filled piston andcylinder type suspension mechanism pertains to the build up of heat inthe cylinder fluid as a result of inadequate dissipation of heat fromthe fluid volume contained within the cylinder. In all known liquidfilled suspension mechanisms a moderate increase in temperature of theworking fluid will cause thermal expansion resulting in changes in theride height of the vehicle frame. Sufficient extension of the piston androd structure may occur to a point where adequate stroking of thecylinder and piston cannot be accomplished under all vehicle operatingconditions thereby resulting in possibly severe damage to the suspensionsystem and other parts of the vehicle. Moreover, excessive extension ofthe suspension mechanism also results in over contraction or telescopicmovement of the piston into the cylinder resulting in very severe fluidpressure conditions in the mechanism when hitting a rough terraincondition and thus creating higher loads on the fluid seals and thecylinder structure. The thermal loading found on prior art type liquidsuspension mechanisms also contributes to degradation of the fluid sealscausing leakage of fluid from the interior chambers of the mechanismsand ultimate failure of the mechanism or at least requiring frequentfluid recharging. Such characteristics are, of course, unwanted invehicle suspension systems, but have heretofore not been dealt within asatisfactory manner.

One of the most severe vehicle suspension system applications is inrelatively large off-highway trucks for hauling earth, mineral ores andvarious other materials and structures. Since this type of vehicle isexpensive to manufacture and maintain and operates virtually at alltimes over very rough terrain, the provision of a spring and suspensiondampening device having a suitable spring rate and being capable ofcomplying with and dampening very severe shock loads on the vehicle ishighly desired. The ability to provide a suspension spring and vibrationdampener which will reduce stresses on the vehicle frame, the suspensioncomponents and tires, as well as permit increased vehicle operatingspeeds, can provide significant economic advantages.

Another problem associated with hydraulic cylinder and piston typevehicle suspension mechanisms, and actuators subject to similarpressures and force loadings, pertains to the provision of piston roadseals which will suitably withstand the very high hydraulic pressuresand the high rates of loading and unloading, or increase and decrease,respectively, of the fluid pressures. The provision of seals which willadequately prevent leakage of fluid over a satisfactory life span of thecoponent without scoring the piston rod and without premature sealfailure has been a longstanding problem and is particularly aggravatedin applications where cyclical movement of a piston rod in a cylinder atrelatively high rates is encountered. In accordance with the presentinvention, however, improved piston rod seals are provided which areparticularly adapted for applications for sealing cyclically andseverely loaded mechanisms such as liquid suspension and vibrationdampener mechanisms.

SUMMARY OF THE INVENTION

The present invention provides an improved hydraulic suspension springand vibration dampener mechanism particularly adapted for use in severeduty applications such as in the suspension systems of off-highwaytrucks and other vehicles.

In accordance with one aspect of the present invention there is provideda suspension spring and vibration dampening mechanism comprising acylinder and piston apparatus which is filled with a compressibleliquid, preferably a silicone composition, which has a suitablecompressibility factor and the cylinder and piston are configured toprovide for two opposed cylinder chambers divided by the piston memberwherein fluid may be transferred directly between the opposed chambersin a high rate cyclic manner without increasing the temperature of thespring fluid significantly.

In accordance with another aspect of the present invention there isprovided a suspension and vibration dampening mechanism of the hydrauliccylinder and piston type wherein fluid is transferred between chambersin the cylinder member in such a way as to provide improved heattransfer from the fluid to the exterior of the cylinder and to preventsubstantial mixing of the transferred fluid with the main body of fluidin the cylinder.

In accordance with a further aspect of the present invention there isprovided a unique cylinder and piston type suspension spring mechanismhaving an improved liquid valving arrangement wherein resistance totransfer of liquid between opposed chambers in the cylinder iscontrolled to dampen oscillating movement of the spring load and to alsoprovide for directing the flow of spring liquid radially outward towardthe cylinder walls to improve the heat transfer characteristics of themechanism. The liquid valving structure includes a generally cylindricalmember slidably mounted on the piston rod and including a portionmovable into a cavity formed in the cylinder head at the rod end of thecylinder to form an improved piston retardation chamber or dashpot.

In accordance with still a further aspect of the present invention thereis provided an improved linearly extensible cylinder and piston typehydraulic spring mechanism and the like having a piston rod sealparticularly adapted to withstand very high rate of increase and highintensity pressure loading while permitting rapid oscillatory movementof the piston rod with respect to the seal. The configuration of theseal and the structure for supporting the seal in the cylinder headminimizes the chance of seal leakage and reduces the mechanical loadingand fluid flow impingement on the seal proper.

The present invention further provides an improved vehicle suspensionsystem wherein the spring structure comprises a wheel assembly support,an improved wheel support suspension spring and a suspension vibrationdampener in a single structural assembly which is durable, is easilyinterchanged, if necessary, for replacement or repair and may beselectively controlled to change the nominal ride height of the vehicleframe with respect to the undercarriage.

Although the present invention is directed primarily to an improvedhydraulic suspension spring and vibration dampener mechanism for use inconnection with off-highway trucks and similar types of vehicles it willbe appreciated by those skilled in the art that the present inventionmay be used in conjunction with on highway vehicles as well as in otherapplications requiring the absorption and dampening of relatively highfrequency and high amplitude cyclical forces. The above-describedfeatures and advantages of the present invention together with furthersuperior aspects thereof will be appreciated by those skilled in the artby reading the detailed description which follows in conjunction withthe drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation of an off-highway dumper truck having asuspension system including an improved suspension spring and dampenermechanism of the present invention;

FIG. 2 is a rear end view of the truck illustrated in FIG. 1;

FIG. 3 is a longitudinal central section view of one of the suspensionspring and dampener mechanisms of the type used on the truck illustratedin FIGS. 1 and 2;

FIG. 3A is a section view taken along line 3A--3A of FIG. 3;

FIG. 3B is a section view taken alog line 3B--3B of FIG. 3;

FIG. 4 is a detail section view showing the suspension spring piston andflow control valve in their relative positions when the mechanism isbeing telescoped or contracted to accommodate upward displacement of thesuspension which it supports;

FIG. 5 is a detail section view similar to FIG. 4 and showing therelationship of the piston and flow control valve structure when thepiston rod is being extended with respect to the spring cylinder;

FIG. 6 is a longitudinal central section view of an alternate embodimentof a suspension strut in accordance with the present invention;

FIG. 6A is a detail section view of a portion of the piston of theembodiment shown in FIG. 6;

FIG. 7 is a detail section view of an improved piston rod sealarrangement for the suspension spring mechanism of the presentinvention;

FIG. 8 is a detail section view of another embodiment of an improvedpiston rod seal for the suspension spring mechanism of the presentinvention;

FIG. 8A is a detail section view on a larger scale of a portion of thepiston rod seal shown in FIG. 8;

FIG. 9 is a detail view of a vehicle suspension mechanism includinganother alternate embodiment of a suspension spring mechanism inaccordance with the present invention;

FIG. 10 is a longitudinal central section view of still anotheralternate embodiment of a suspension spring mechanism;

FIG. 11 is a longitudinal view, partially sectioned and broken, showinga third alternate embodiment of the suspension spring mechanism of thepresent invention; and

FIG. 11A is a detail section view on a larger scale of a portion of thecylinder sleeve and cylinder of the embodiment of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description which follows like parts are marked throughout thespecification and drawing figures with the same reference numerals,respectively. The drawings are not necessarily to scale and certainfeatures of the invention may be shown in schematic form in the interestof clarity and conciseness.

In the description which follows and as illustrated in the drawing theimproved vibration isolator and dampener apparatus of the presentinvention is particularly configured for use as a suspension spring fora vehicle and also known as a suspension strut. One of the most severeduty applications for vibration isolators or springs for land vehiclesis in a vehicle such as an off highway material hauler of the typeillustrated in FIG. 1 and generally designated by the numeral 16. Thevehicle 16 is characterized as a so-called dumper truck of a size whichis capable of hauling from 50 to 200 tons of material such as varioustypes of mineral ore or earth overburden which must be moved frompoint-to-point over very rough terrain. These vehicles represent verylarge capital investments and their operation must not be compromised bysubstantial down time or reduced operating speed as a result of poorlydesigned suspensions. Suspension systems for vehicles of this type whichdo not permit operation at optimum speed also contribute to driverfatigue as well as to early failure of vehicle frame components,suspension components and tires. Accordingly, it is of importance toprovide such a vehicle with a suspension system which is capable ofisolating the displacement of the vehicle undercarriage with respect tothe load supporting frame and to dissipate the energy generated bydisplacement of the vehicle suspension system without rapidly degradingthe suspension isolator and dampener itself. In this regard asubstantially improved vibration isolator or spring is provided in theform of a cylinder and piston type suspension strut in accordance withthe present invention.

Referring to FIGS. 1 and 2, the dumper truck 16 comprises a main frame18 for supporting a material containing body or bed 20, a driver cab 22and an engine housing 24. The frame 18 is supported by independentlysuspended front steering wheels 26, one shown, mounted on trailing armsuspension members 28, one shown, pivotally connected to the frame 18 at30.

As shown in FIG. 2 also, the truck 16 typically includes a rear dualwheel and axle assembly 32 which is pivotally connected to the frame at34, FIG. 1, by a suitable bearing which will permit limited pivotalmovement about a horizontal transverse axis and a horizontallongitudinal axis. In accordance with the present invention thesuspension system for the truck 16 includes improved cylinder and pistontype vibration isolating and dampening suspension springs or struts,generally designated by the numerals 36 and 38, respectively. The struts36 and 38 are of substantially identical configuration but may be sizedaccording to the weight to be supported at the respective ends of theframe 18. The suspension struts 36, one shown in FIG. 1, areinterconnected between the frame 18 and the suspension arms 28 at theiropposite ends respectively. The suspension struts 38 are also similarlysuitably connected at their opposite ends to the vehicle frame 18 and tothe wheel and axle assembly 32 at pivot connections 44 and 46, FIGS. 2and 3, respectively. The suspension struts 36 and 38 advantageouslycombine the function of a vibration isolator or spring with adisplacement or vibration dampening means for permitting displacement ofthe wheel and axle assemblies 26 and 32 without transmittingdisplacement or severe stresses to the frame 18. The suspension struts36 and 38 also provide for operation in an improved damping factor rangewhich reduces loading on the vehicle wheel and axle assemblies and othercomponents making up the suspension system of the truck 16.

Referring now to FIGS. 3 through 5, in particular, a preferredembodiment of a vibration isolating and dampening suspension strut isillustrated in detail. For the sake of description herein the suspensionstrut illustrated in FIGS. 3 through 5 will be assumed to be one of thesuspension struts 38. However, the suspension struts 36 may be ofsubstantially similar design but sized to accommodate the supporting anddampening requirements of the front wheel suspension of the truck 16.

The suspension strut 38 preferably comprises an elongated cylindricaltubular cylinder member 48 having a first head portion 50 which may beformed separate from the cylinder 48 and threadedly engaged therewith bycooperating threads 52. The head portion 50 is suitably formed toinclude a tongue portion 54 interposed between spaced apart clevisportions 55, one shown, forming the pivot connection 46 and including aspherical bearing assembly 47, as shown by way of example for the pivotconnection 44 in FIG. 3. The cylinder 48 is characterized by acylindrical bore defined by a bore wall 56 and is closed at the endopposite the head 50 by a second head member 58 of similar configurationand threadedly engaged with the cylinder 48 by cooperating threads 60.The suspension strut 38 includes a cylindrical piston 62 slidablydisposed in the cylinder bore and dividing the bore into opposed fluidchambers 64 and 66. The piston 62 is retained on an elongated piston rod68 having a reduced diameter portion 70 on which the piston 62 isdisposed and retained thereon by a nut 72. The piston rod 68 extendsinto the cylinder 48 and is extensible and retractable with respect tothe cylinder.

The piston rod 68 includes a separable head portion 74 having spacedapart clevis members 76 between which a tongue part 78 extends and formspart of the vehicle frame 18. A suitable pivot pin 80 and the bearingassembly 47 form the pivot connection 44 between the strut 38 and theframe 18. The piston rod 68 is secured to the head portion 74 by anaxially extending reduced diameter rod portion 69 which is threadedlyengaged with a nut 81. The head portion 74 is suitably secured inassembly with an axially extending tubular sleeve member 82 by fasteners83. The sleeve 82 is dimensioned to extend in telescoping relationshiparound the outer circumference of the cylinder 48 to form a shield forthe portion of the piston rod 68 extending from the cylinder head 58 andto provide means for pumping ambient air into and out of a chamber 84formed between the sleeve 82, the piston rod 68 and the cylinder 48. Aresilient cushion member 86 is suitably secured to a transverse upwardlyfacing wall of the head member 58.

The piston and piston rod assembly 62-68 is supported for reciprocalsliding movement in the cylinder 48 on an enlongated sleeve bearing 88disposed in a suitable recess in the head 58 and a sleeve bearing 90disposed around the periphery of the piston 62. The sleeve bearings 88and 90 may be made of a suitable self-lubricating material such as atypical bearing metal or a filled fluorocarbon plastic. The piston 62 isalso provided with a cylindrical piston ring type seal 92 disposedaround its periphery and slidably engaged with the bore wall 56 toprovide a substantially fluid-tight seal between the chambers 64 and 66.The suspension strut 38 functions as a spring and a vibration oroscillation dampening device in combination and is preferably operableto be filled with liquid silicone such as a Series 200 silicone fluidhaving a viscosity of 1000 centistokes at 67° F. and commerciallyavailable from Dow-Corning Corporation, Midland, Mich. The liquidintroduced into chamber 64 and allowed to flow into chamber 66 by meansto be described herein may be provided through a suitable valve 94 inthe head 50.

The chamber 64 and 66 are in fluid flow communication with each other byway of passage means formed in the piston 62 and comprising a pluralityof elongated passages 96 opening to a transverse piston end face 63facing the chamber 66 and to a radially extending annular flow channel98 opening into the chamber 64 and formed by an integral piston bafflepart 65. The passages 96 are preferably in sufficient number as toprovide for a suitably restricted flow of liquid from the chamber 64 tothe chamber 66 when the piston 62 and rod 68 are being retracted intothe cylinder 48 under a load imposed on the suspension strut. The weightof the vehicle frame and other components supported by the struts 38results in compression of liquid in the chambers 64 and 66. Furtherloading on the strut tending to retract or telescope the piston rod 68into the cylinder 48 causes additional compression of the liquid andtransfer of the liquid from the chamber 64 to the chamber 66.

In accordance with an important aspect of the present invention thesuspension strut 38 includes means for controlling the flow of fluidfrom the chamber 66 to the chamber 64 to increase the resistance of flowof fluid in that direction versus the resistance to flow from thechamber 64 to the chamber 66. The suspension strut 38 includes a valvemember comprising a generally cylindrical sleeve 100 extending insleeved relationship around the piston 62 and between the piston endface 63 and a transverse shoulder 71 formed on the piston rod 68 betweenthe main portion of the rod and the reduced diameter portion 70. Thevalve member 100 includes a cylindrical hub portion 101 and a radiallyextending circular flange portion 102 which is adapted to be engagedwith the transverse face 63 along a cooperating surface 103. The valvemember 100 is freely axially movable on a cylindrical spacer 105disposed over the rod portion 70 between the piston 62 and the shoulder71. The valve member 100 includes a plurality of circumferentiallyspaced apart elongated passages 104 which extend axially through the hubportion 101. The passages 104 are adapted to be in communication with anannular channel 97 formed in the piston face 63 and in communicationwith the passages 96. The passages 104 are preferably four in number,FIG. 3B, or otherwise provide an effective cross-sectional flow arealess than the cumulative cross-sectional flow area of the passages 96 soas to increase the resistance of flow of fluid from the chamber 66 tothe chamber 64 which must be by way of the passages 104, the flowchannel 97 and the passages 96.

Referring particularly to FIG. 5, the suspension strut 38 also includesan improved high pressure seal assembly including a generally annularseal member 100 disposed in a cavity 112 formed in the head 58 insurrounding relationship to the circumferential polished outer surface113 of the piston rod 68. The seal member 110, which is preferablyformed of a fluorocarbon plastic, includes a transverse end face 114disposed in abutting engagement with a cooperating end wall 115 of thecavity 112. The seal member 110 includes a circumferential cantileverbeam lip portion 118 having an inner circumferential surface 120operable to be in sliding engagement with the surface 113 of the pistonrod. The beam portion 118 forms a cavity 122 with the remainder of thebody of the seal member 110 and is engageable with a circumferentialelastomeric o-ring member 124 disposed around and engageable with thebeam portion 118 and operable to deflect the beam portion into forcibleengagement with the piston rod 68. A suitable groove 125 is formed inthe seal member 110 or may also be formed in the o-ring 124 to allowfluid to enter the cavity 122 from chamber 66 except when the piston 62is in the position shown in FIG. 5. Accordingly, under normal operatingconditions, when the piston rod 68 is not fully extended, pressure fluidmay act on the beam portion 118 of the seal member 110 to bias the sealsurface 120 into forcible engagement with surface 113.

Referring further to FIG. 5, the seal member 110 is of a uniqueconfiguration wherein a radially outwardly relieved conical surface 117is formed on the seal member between the end face 114 and the piston rodcircumferential surface 113. This radially relieved conical surface orramp 117 prevents no more than the desired amount of surface areadefined by the surface 120 from forcibly engaging the piston rod surface113. Fluid pressure acting on the transverse axially projected area ofthe seal member 110 facing the chamber 66 will tend to rotate the sealso that the surface 117 comes into engagement with the surface 113. Thisis alleviated by the radically outwardly relieved conical configurationof surface 117. When the rod 68 is being extended to increase thepressure in the chamber 66 this pressure is also present in the cavity140 and tends to squeeze the beam portion 118 radially inward intoengagement with the rod surface 111 to effect a fluid-tight seal. Theresilient o-ring 124 functions only as a stressing ring to maintain aradially inwardly directed squeeze on the beam member 118 sufficient toprovide low pressure sealing between the surfaces 120 and 113. A secondo-ring member 128 is suitably retained in a circumferential groove inthe seal member 110 and the seal member 110 is retained in the cavity112 by a retaining ring 130 secured to the head member 58 by socket headscrews 132.

The screws 132 also retain a second retaining ring 134 which operates tosecure a cylindrical seal ring 136 in a counterbore 138 formed in thering 130. The seal ring 136 is preferably formed of an elastic materialsuch as nylon and is operable to engage the outer circumferentialsurface of the hub portion 101 to form a cavity 140 between the hubportion and the seal 110 which is effectively sealed from the chamber 66when the valve member 100 enters into engagement with the seal ring 136.The counterbore 138 is of slightly larger diameter than the outerdiameter of the seal ring 136 to permit radial expansion of the sealring upon engagement with the hub portion 101. The seal ring 136 and thehub portion 101 are preferably formed with cooperating beveled surfacesto facilitate engagement. A relief passage 142 is formed in the flange102 of the valve member 100 and is operable to communicate the chamber66 with the flow passages 97 and 96 to serve as the sole passage meansbetween the chambers 66 and 64 when the valve member 100 is engaged withthe seal ring 136 as shown in FIG. 5.

The axially slidable valve member 100 together with the construction ofthe piston 62 and the passages 96, 97 and 98 provide for a substantiallyimproved hydraulic suspension strut for off-highway as well asover-the-highway vehicles and for other applications as will beappreciated by those skilled in the art. By using a fluid such as thesilicone liquid referenced herein in the chambers 64 and 66 thesuspension strut 38 may be precharged with fluid to position thesupported load in such a way that the strut is normally under light orempty weight load operating with its piston 62 and piston rod 68 in thenominal position illustrated in FIG. 3. Under this operating conditionthe silicone liquid has undergone approximately 6% compression of itstotal compressibility of 18%. When the vehicle 16, for example, is fullyloaded the strut 38 will be forced to retract its piston 62 and rod 68further into the chamber 64 further compressing the silicone liquid todecrease its volume by an additional 6%. This leaves effectively 12% and6% compression, respectively, for reciprocation of the piston 62 and rod68 when the vehicle is unloaded and fully loaded, respectively.

One of the major problems associated with the use of a hydraulicsuspension spring strut and, in particular, with the use of liquidsilicone is the thermal volumetric expansion and contraction of theliquid. Under relatively severe duty cycle applications of thesuspension strut 38 the transfer of fluid between the chambers 64 and 66through the restricted flow passages in the piston 62 and the valvemember 100 will result in substantial heating of the fluid.Additionally, the rubbing action of the bearing sleeves 88 and 90, theseal member 110, the seal 92 and the wiper ring 143, FIG. 3, will alsogenerate heat which eventually is transferred to the substantialquantity of fluid in the chamber 64 during operation of the strut.Heating of the silicone liquid will change its viscosity as well asresult in expansion of the liquid which will change the ride height ofthe vehicle, possibly resulting in full extension of the piston rod 68into the position wherein the valve flange 102 is engaged with theretaining ring 134. Accordingly, it is important to maintain the mainbody of fluid in the chamber 64 at or near the ambient temperature or atleast prevent substantial heating of the fluid which could result indegradation of the various seal members for the strut 38 and seriouslyaffect the ride height of the supported vehicle with respect to itsundercarriage.

Referring particularly to FIGS. 3 and 4, the relationship of the piston62 with respect to the valve member 100 is illustrated in the respectiveconditions when the piston and piston rod assembly is being extendedfrom the cylinder 48 and retracted into the cylinder under cyclicloading of the suspension strut 38. In FIG. 4 the piston 62 and thevalve member 100 are shown in their positions relative to each otherwhen the piston and piston rod 68 are under a load tending to telescopeor retract the piston rod into the cylinder bore. Under thesecircumstances the fluid in chambers 64 and 66 is being compressed andfluid is flowing from the chamber 64 to the chamber 66 through theannular flow channel 98, the passages 96 and the annular groove 97.Since the chamber 64 is contracting while the chamber 66 is tending toexpand fluid flowing between these chambers will force the valve member100 against the shoulder 71 to define an annular flow channel betweenthe faces 63 and 103 wherein fluid entering the chamber 66 will flowradially outward toward the bore wall 56. Accordingly, during retractionof the piston and piston rod into the cylinder 48 the flow of liquidfrom the chamber 64 to the chamber 66 is restricted primarily by theflow channel 98, the passages 96 and the flow channel formed between thefaces 63 and 103 and, upon leaving the annular channel between thesefaces, the fluid impinges the cylinder bore wall 56 and tends to flowalong the wall as indicated by the directional arrows in FIG. 4. Thanksto the direction of flow of the fluid imposed by the formation of theflow channel between the surfaces 63 and 103, the fluid is brought intoheat exchange relationship with the cylinder 48 and heat is transferredto the cylinder outer surface 49.

Referring to FIG. 3, when the strut 38 is undergoing a rebound orextension of the piston 62 and piston rod 68 with respect to thecylinder 48 fluid in the chamber 66 flows to the chamber 64 and thepressure differential created thereby will move the valve member 100into the position illustrated with the surfaces 63 and 103 in abuttingand substantially fluid sealing engagement. Accordingly, fluidtransferring from the chamber 66 to the chamber 64 must flow through thepassage 104, the channel 97, the passages 66 and is then directedradially outwardly towards the bore wall 56 as it flows through thechannel 98. Thanks also to the valve member 100, the resistance to flowof fluid from the chamber 66 to the chamber 54 is greater than in theopposite direction and the cyclic extension and retraction of the pistonwith respect to the cylinder 48 is dampened during the extension orrebound portion of the spring oscillation cycle. The substantial heatingof the silicone fluid as it is forced through the passages 104, 97 and96 is dissipated by contact of the fluid along the bore wall 56 as itpasses through the annular flow channel 98 and is turned to flow alongthe borewall 56 into the chamber 64. Accordingly, fluid flowing into thechamber 64 does not floor directly into the main body of fluid in thecenter of the chamber but first contacts the borewall 56 of the cylinder48 to transfer a substantial portion of its heat to the cylinder whichdissipates heat to the atmosphere surrounding the suspension strut 38.The cooling action on the fluid within the chambers 64 and 66 is furtherenhanced by a pumping action of the piston rod head 74 and the sleeve 82as the piston rod moves with respect to the cylinder 48 and air ispumped into and out of the chamber 84. The flow of air into and out ofthe chamber 84 is along the outer wall 49 to enhance heat transfer awayfrom the cylinder 48 and the fluid contained within the chambers 64 and66.

In the event that the piston and piston rod assembly are extended withrespect to the cylinder 48 sufficiently such that the valve member hub101 engages the seal ring 136, as indicated in FIG. 5, fluid may escapefrom the chamber 66 only through the passage 142. Accordingly, once thevalve member 100 has moved into sealing engagement with the ring 136further movement of the piston 62 to extend the rod 68 from the cylinderis substantially retarded by entrapment of fluid in the cavity 66.Moreover, when the valve member 100 moves into sealing engagement withthe ring 136 fluid pressure acting on the seal 110 is maintained at alevel no more than is present in the chamber 64 and the seal 110 is notexposed to the substantial increase in pressure experienced in thechamber 66. The seal member 110 is also substantially protected fromconvective fluid flow in the cavity 140 by a radially inward extendingbaffle portion 131 of the retaining ring 130.

The above-described unique structure provided by the hydraulicsuspension strut 38 has enabled the provision of a strut having adamping factor or ratio of approximately 0.4 to 0.6 without thedetrimental effects of thermal degradation of the strut or erraticchanges in ride height of the strut. The redirection of the flow offluid between the chambers 64 and 66 to provide heat transfer away fromthe main body of the fluid in the respective chambers and the uniqueflow restricting valve 100 provides a superior combination vibrationisolator or spring and spring dampener producing the benefits describedabove for use in conjunction with land, off-highway vehicles, inparticular.

The suspension strut 38 as well as the other embodiments disclosedherein is particularly adapted for use as a vehicle suspension componentbut the salient features of the invention also provide for use of thesuspension strut in other vibration isolation and damping applications.Moreover, as indicated above, the improved suspension strut 38 alsoprovides for adapting the strut to operate with a damping ratio in therange of approximately 0.4 to 0.6 whereas prior art suspension strutsincluding combination hydraulic-pneumatic types can operate only in adamping ratio range of about 0.2 to 0.25 maximum. The damping ratio isthe ratio of the damping constant of the particular system in questionto the damping constant of a critically damped system, that is, one inwhich the maximum ratio of diminishing amplitude of vibration occurs.The damping ratio and the damping constant are discussed by Ralph Burtonin Vibration and Impact, Dover Publications, Inc., New York, 1968.

Referring now to FIG. 7, another embodiment of a piston rod sealarrangement in accordance with the present invention is illustrated indetail and includes a tandem arrangement of two generally cylindricalseal body members 160 adapted to be disposed in respective counterbores161 formed in a seal insert 163 which is suitably supported in a bore112a formed in a modified head member 58a. The seal body members 160each include a radially outwardly relieved conical surface 162, agenerally cylindrical inner sealing surface 164, an inner annularcounterbore 166 and an outer circumferential annular recess 168. Aresilient o-ring type stress ring 170 is disposed in the recess 168 andis operable to bias the seal body 160 radially inwardly in sealingengagement with the surface 113 of the piston rod 68. The seal assemblyillustrated in FIG. 7 is retained in the bore 112a by a modifiedretaining ring 171 having an axially projecting hub portion 172 which isdimensioned to provide a small axial space between opposed surfaces 174and 176. A shoulder 165 provides a similar space between surfaces 175and 176 of the second seal assembly. Each seal body 160 is also backedby a substantially rigid ring 180 having an inner lip 182 forming asealing line with the surface 113.

When the piston rod 68 is being retracted into the cylinder the reducedpressure in the cavity 66 will result in the primary sealing effort ofthe surfaces 164 being carried out by a radially inward squeezing on theseal body 160 due to the elastic memory of the o-rings 170. Fluidpressure in the cavity 66 also acts on the seal body inner and outercircumferential surfaces defining counterbore 166 as well as the recess168 and on the o-ring 170 to form opposing forces which are balanced inaccordance with the extent of the opposing surface areas so that acontrolled amount of sealing force is exerted on the seal body 160 tosqueeze it radially inwardly. Moreover, the generous transverse surfacearea of the seal body face 177 and the conical relief surface 162together with the substantially rigid ring 180 also minimizes thetendency for the body 160 to tilt or extrude out of the seal cavity.

Referring now to FIGS. 8 and 8A, an alternate embodiment of a piston rodseal for the suspension strut 38 is illustrated. In the seal arrangementillustrated in FIGS. 8 and 8A a generally cylindrical seal body 200 isprovided with an inner cylindrical sealing surface 202 and a radiallyoutwardly relieved conical ramp surface 204. A circumferentialcounterbore 206 and opposed outer recesses 208 and 210 are also formedin the body, wherein the latter recess is adapted to receive a resiliento-ring member 212. The axial depth of the recess 210 with respect to thelongitudinal axis of piston rod 68 is less than the relaxed diameter ofo-ring 212. A cylindrical rigid back up ring 214 similar to the back upring 180 is also disposed in the recess 112 between the seal body 200and the transverse end wall 115. A modified retaining ring 130a isutilized in the seal arrangement illustrated in FIG. 8 and includes aradially inward projecting baffle 131a. Inner and outer circumferentialsurfaces 207 and 209 are proportioned to provide opposing radiallydirected forces acting on the seal body to assist in controlling theforce acting on the rod 68 by the sealing surface 202. At the same timethe axially projected face area of the body 200 exposed to high pressurefluid will effect movement of the body toward the back up ring 214whereby the squeeze on the o-ring 212 is effective to cause radialinward squeezing action on the body 200 controlled in accordance withthe dimensions of the recess 210 in relation to the volume of the o-ring212.

Accordingly, as shown in FIG. 8A, pressure fluid acting on the axiallyprojected annular area A_(s) of the seal body 200 between the surface202 and the outer peripheral edge of the body will deflect the o-ring212, as indicated by the dotted lines in FIG. 8A, as the seal body movestoward engagement with the ring 214 also indicated by dotted lines. Thisdeflection of the o-ring 212 will increase a radially inward forceacting on the seal body 200 to increase the sealing effect of surface202 on surface 113 as pressure in the cylinder chamber 66 increases. Theeffective area A_(s) may be diminished somewhat by fluid leaking pastthe seal body outer surface into the recess 210 but this area will stillbe sufficient to cause a force acting on the seal body 200 to move ittoward the alternate position.

Referring now to FIGS. 6 and 6A, an alternate embodiment of a suspensionstrut in accordance with the present invention is illustrated in detailand generally designated by the numeral 238. The suspension strut 238includes a cylinder 48, and a piston rod 68 extending there into anddividing the interior of the cylinder bore into chambers 264 and 266 bymeans of a piston 262. The piston 262 is secured to the rod portion 70by nut 72 in the same manner as the piston 62. The piston 262 includespassage means for communicating the cylinder chambers 264 and 266comprising a plurality of spiral grovoes 270 formed on the outercircumference of the piston 268 and extending between opposed end faces272 and 274. The grooves 270 may, for example, be characterized asdouble or triple thread grooves so that adjacent grooves shown are eachin parallel communication with the chambers 264 and 266. The grooves 270thus communicate working fluid between the chambers 264 and 266 when thepiston 262 and piston rod 68 are being extended from or telescoped intothe cylinder 48. The cross-sectional profile of the grooves 270 in aplane parallel to the longitudinal axis 239 of the suspension strut 238is illustrated in FIG. 6A wherein each of the grooves 270 has a firstflank 276 extending in a plane substantially normal to the axis 239 anda second flank 278 extending at an acute angle with respect to the axisand including a curved portion 279 forming a somewhat venturi shapedorifice between the flank and borewall 56. Accordingly, when the piston262 is moving in the direction to transfer fluid from the chamber 264 tothe chamber 266 fluid will flow through the grooves 270 between pistonend faces 263 and 265. Fluid will also tend to flow from one groove 270to another in meeting somewhat less resistance thanks to the slopingflanks 278-279 which form a plurality of venturilike flow passagesbetween the bore wall 56 and the peripheral surface of the piston 262.

On the other hand when the piston 262 is moving toward the cylinder head58 to transfer fluid from the chamber 266 to the chamber 264 asubstantially sharp edged orifice is presented between adjacent grooves270 due to the transverse flanks 276. This configuration forms asomewhat labyrinth type seal between the periphery of the piston 262 andthe bore wall 56 and presents a greater resistance to fluid flow whenthe piston rod 68 is extending from the cylinder 48 and increasing thevolume of the chamber 264 to perform the strut damping function.Moreover, fluid transferring between the chambers 266 and 264 throughthe spiral grooves 270 and between the grooves 270 is constantly flowingin intimate contact with borewall 56 to transfer heat generated in andby the fluid to the cylinder 48 for transfer to the surface 49 and tothe environment in which the suspension strut 238 is operating.

The piston 262 includes an integral axially extending hub portion 280 inplace of the sliding valve member 100 and which is adapted to extendinto a cavity 240 in sliding engagement with the seal ring 136 to form adashpot or cushion to prevent violent engagement of the piston 262 withthe head 58. A passage 241 extends from the end face of the hub portion280 to the face 265 of the piston 262 to limit fluid pressure buildup inthe cavity 240 when heh hub portion 280 moves into sealing engagementwith the seal ring 136. The piston 262 is also provided with a flowseparating shield 282 secured to the piston rod by the nut 72 to form asubchamber 269 and to prevent substantial mixing of fluid entering thechamber 264 with the main body of fluid already present in that chamberduring transfer of fluid from the chamber 266. The piston 262 is notprovided with a bearing ring; however, circumferential flank surfacesformed by axially extending surface portion 281 of the flank portions279 may be coated with an anti friction coating and the clearancesbetween the piston 262 and the borewall 56 may be such as to form somebearing support if lateral loading on the rod 68 is extreme.

As previously mentioned the suspension strut of the present inventionmay also be adapted for use in connection with over-the-road automotivevehicles. Referring to FIG. 9, for example, there is illustrated aportion of a rear wheel independent suspension system for an automativevehicle including a chassis or frame 300 and a control arm 302 pivotallyconnected to the frame and to a wheel spindle 304. Another embodiment ofthe suspension spring mechanism or strut of the present invention isshown connected to the spindle support 305 and is generally designatedby the numeral 306. The suspension strut 306 includes a cylinder 307which is modified to be suitably connected to the spindle support 305and is pivotally connected at its upper end at 309 to the frame 300. Thestrut 306 is substantially identical to the strut 38 except formodification of the cylinder distal end to accommodate the particulartype of vehicle structure to which it is connected. The suspension strut306 conveniently replaces the combination coil spring and so calledshock absorber structure for both steering and non steering wheelsuspensions conventionally known as a MacPherson type suspension unit.

Referring now to FIG. 10, there is illustrated another embodiment of asuspension spring mechanism or strut in accordance with the presentinvention and generally designated by the numeral 338. The suspensionstrut 338 includes a cylinder 348 similar to the cylinder 48 butincluding an integral extended portion 350 including a bore 351 forreceiving a swivel shaft portion of a wheel spindle, not shown. A piston62 and a piston rod 368 of the suspension strut 338 are slidablydisposed in a bore defined by a cylindrical borewall 356 to divide theinterior of the cylinder 348 into opposed chambers 364 and 366. Thepiston 62 is secured to a rod portion 370 by a nut 72. The chamber 364is closed at its lower end by a head member 369 and the upper end of thecylinder 348 is closed by a head member 358 having a resilient cushionmember 372 secured thereto. The piston rod 368 is secured to a rod headportion 374 which in turn is secured to a cylindrical heavy walledsupport housing 376 having an elongated cylindrical bore 380 forreceiving the cylinder 348 in telescoping sleeved relationship thereto.

The housing 376 includes spaced apart sleeve bearings 382 disposed inthe bore 380 for slidably supporting the cylinder member 348 withrespect to the housing 376. The housing 376 may be adapted to be rigidlysecured to suitable support structure, not shown, by a mounting flange377. Accordingly, the suspension strut 338 may comprise not only avibration isolating spring and dampening structure for a wheel unit butcomprise the sole supporting structure for the wheel unit. The slidingvalve member 100 is disposed on a spacer 365 secured between a shoulder371 and the piston end face 63. The spacer 365 has a transverse shoulder367 engageable with the valve member 100 to limit its travel away fromthe piston end face 63. The psiton rod 368 may have a smaller outerdiameter since it is not required to support lateral loads. The otherinternal structure of the suspension strut 338 is substantiallyidentical to the strut 38 and is not believed to require furtherdetailed description to enable one to practice the invention embodiedtherein. Thanks to the substantial volume of liquid silicone which maybe introduced into the cylinder chambers the strut 338 as well as thestruts 38 and 238 provide improved combination spring or vibrationisolation structures and vibration damping means in a single hydrauliccylinder and piston type structure. The suspension strut 338 may befilled with fluid through a suitable fill valve 382 in communicationwith a passage, not shown, extending through the piston rod 68 andopening into the chamber 364.

Referring now to FIGS. 11 and 11A, another embodiment of a suspensionstrut in accordance with the present invention is illustrated andgenerally designated by the numeral 438. The suspension strut 438 ischaracterized by an elongated cylinder member 440 having an internallythreaded portion 442 at one end for receiving in threaded engagement ahead member 444. The cylinder 440 is characterized by a longitudinalcylindrical bore defined by a cylindrical borewall 446 having anintermediate stepped portion 448 between the borewall 446 and thethreaded portion 442. The intersection of the borewalls 446 and 448forms a shoulder 450. The cylinder 440 is adapted to be secured to alower head member 50 in the same manner as the suspension strut 38.

An elongated cylindrical sleeve member 452 is disposed in the bore ofthe cylinder 440 and is secured therein between the head member 444 andthe shoulder 450. The sleeve 452 includes spaced apart bearing portions454 and 456 which are in close fitting engagement with the borewall 446.The suspension strut 438 also includes a piston rod 68 which is securedat its distal end to a modified piston 458 slidably disposed within thesleeve member 452 in close fitting and substantially fluid sealingengagement with the inner borewall 460 of the sleeve. The piston 458 issecured on the rod 68 by a nut 72. The rod 68 is secured to a headportion 74 and supporting the outer tubular sleeve 82 in the same manneras the suspension strut 38.

The piston 458 is slidably disposed in the sleeve 452 and is preferablyformed with a suitable low friction coating on the exterior surface toform a suitable bearing surface for engagement with the borewall 460.The piston 458 includes a reduced diameter hub portion 459 which isoperable to engage the seal ring 136 in the same manner as theembodiments of the suspension strut described in conjunction with FIGS.3 and 6 herein. The modified head 444 is also adapted to receive thepiston rod seal 110 in a suitable cavity 445.

The piston 458 divides the interior of the cylinder 440 into opposedchambers 464 and 466 operable to be filled with the aforementionedsilicone fluid. Fluid is transferred between the chambers 464 and 466through a plurality of spiral grooves 470 formed on the exterior of thesleeve 446 in substantially the same manner as the grooves 270 areformed on the exterior of the piston 262. The grooves 470 may comprise asingle or double or triple thread grooves which open, respectively, toperipheral channels 472 and 474 formed on the sleeve 452. The channel472 opens in to the chamber 466 through a plurality of spaced apartports 476 extending radially between the channel 472 and the chamber466. The channel 474 opens into the chamber 464 through axiallyextending passages 478 formed in the sleeve member bearing portion 456.

Referring to FIG. 11A, the configuration of the grooves 470 issubstantially similar to the grooves formed on the piston 262 of theembodiment illustrated in FIGS. 6 and 6A. The grooves 470 are formed byrespective flank portions 480 which extend substantially in a planetransverse to the longitudinal axis 441 of the suspension strut 438. Thegrooves 470 are also defined by flanks 482 extending at an acute anglewith respect to the axis 441 and including curved portions 483 formingsomewhat venturi shaped orifices between the groove flanks and thecylinder borewall 446.

Accordingly, fluid flowing from the chamber 464 to the chamber 466, inresponse to telescoping movement of the piston 458 into the cylinder440, will occur by the flow of fluid from the chamber 464 through thepassages 478 into the annular channel 474 and then through the spiralgrooves 470 to the channel 472 and then through the ports 476 intochamber 466. Flow in the direction described above will also occurbetween adjacent grooves 470 through the venturilike orifices definedbetween the borewall 446 and the groove flank portions 482-483. Thespiral flow of fluid through the grooves 470 and the axial flow throughthe aforementioned orifices will place the fluid in intimate contactwith the borewall 446 for transfer of heat through the cylinder 440 toits exterior surface 486. Transfer of fluid from the chamber 466 to thechamber 464, in response to extension of the piston rod 68 from thecylinder 440, will cause fluid to flow in substantially the reversedirection to that described above and the resistance to axial flow offluid between adjacent grooves 470 will be increased due to theessentially sharp edged orifices formed between the groove flanks 480and the borewall 446.

The piston 458 is also provided with a pressure relief passage 485extending from the distal end of the piston hub portion 459 to thepiston end face 461. Accordingly, when the hub portion 459 enters intosealing engagement with the seal ring 136 fluid pressure in the cavitybetween the seal ring 136 and the seal member 110 will be relievedthrough the passage 485. Moreover, the axial spacing of the ports 476with respect to the distal end of the piston hub portion 459 is suchthat as the hub portion 459 engages the seal ring 136, the edge of thepiston 458 formed by the transverse end face 463 commences to close offthe ports 476 from communicating with the chamber 466. Accordingly,movement of the piston 458 across the ports 476 creates a throttlingaction as fluid tries to escape from the chamber 466 which is effectiveto form a dashpot or cushion to decelerate movement of the piston andthe rod 68 on an extension stroke from the cylinder 440. One advantageof the arrangement of the suspension strut 438 is that the piston 458 isoperable to support lateral loading imposed on the piston rod 68 and isin bearing engagement with the borewall 460. Lateral bearing loadsimposed on the sleeve member 452 are transferred to the cylinder member440 at the bearing surfaces 454 and 456. The suspension strut 438 alsoprovides means for placing the working fluid in intimate contact withits cylinder member to transfer heat away from the main body of fluid inthe chambers 464 and 466.

The struts 38, 238, 338 and 438 are normally placed in operation on avehicle suspension system by filling the lower cylinder chamber withfluid such as the silicone liquid to extend the piston and piston rodassembly to its limit position with respect to its associated cylinderwhen the suspension strut is under zero load. Suitable vent means, notshown, may be provided to vent air from the cylinder chambers during thefilling operation. The empty weight of the vehicle is then imposed onthe piston and the fluid in the cylinder chambers causing somecompression of the fluid and transfer of fluid to the upper or smallervolume piston chamber. Accordingly, under nominal load conditions, thepiston is positioned a comparatively short distance from the head of thecylinder through which the piston rod extends so that the strut iscapable of sustaining relatively large steady state and impact loads tocompress the liquid in the lower chamber such as the chambers 64, 264,364, or 464 so that the compression or compliance of the fluid willfunction in the manner of a spring with a substantially linear springrate. The suspension spring mechanisms or struts 38, 238, 306, 338 and438 and the piston rod seals described herein are fabricated usingconventional engineering materials used for hydraulic cylinder andpiston type actuators and seal structures except as noted herein.

Although preferred embodiments of the present invention have beendescribed herein those skilled in the art will recognize that varioussubstitutions and modifications may be made to the embodiments disclosedwithout departing from the scope and spirit of the invention as recitedin the appended claims.

What I claim is:
 1. A suspension apparatus for a vehicle for permittingdisplacement of wheel support means relative to a frame of said vehicleand for damping said displacement, said apparatus comprising a hydrauliccylinder and piston assembly, including:an elongated cylinder memberdefining a wall enclosed longitudinal bore and opposed head portions; apiston reciprocably disposed for relative bidirectional movement in saidbore and dividing said bore into opposed fluid chambers, and a pistonrod connected at one end to said piston and extending through one ofsaid chambers and one of said head portions to form a rod end chamberand a second end chamber; piston rod seal means supported by saidcylinder member and including means in fluid sealing engagement withsaid piston rod to prevent leakage of fluid from said one chamber to theexterior of said apparatus; a compressible liquid filling the chambers;means for interconnecting said apparatus between said frame and saidwheel support means whereby said piston and piston rod are forced intothe cylinder until the fluid is compressed sufficiently in said cylindermember to support the vehicle at a normal height dependent upon the loadwhile permitting reciprocating displacement of said wheel support meansin a normal range centered generally about the normal ride height as thevehicle travels over irregular terrain; flow restriction means forpermitting only restricted flow of fluid from one chamber to the otherchamber in response to reciprocation of said piston and piston rod withrespect to said cylinder member to provide for damped reciprocatingdisplacement of said wheel support means in the normal range; said flowrestriction means including passage means formed by said pistonextending between said chambers, and a valve member slidably disposed onsaid piston rod between the piston and the head portion defining the rodend chamber, said valve member being reciprocally shiftable along saidpiston rod in response to reciprocation of said piston relative to thecylinder during the damped reciprocating displacement in the normalrange including restrictive passage means formed thereby and arranged tobe in series flow communication with said passage means in said pistonin one direction of movement of said piston to provide a greaterresistance to fluid flow in one direction between said chambers than inthe other direction.
 2. The apparatus set forth in claim 1 wherein:saidvalve member is movable relative to said piston in the other directionof movement of said piston to provide for communicating said passagemeans in said piston directly with said one chamber, and said valvemember includes a radially extending portion cooperable with said pistonto form passage means for directing the flow of fluid radially outwardlyand along said borewall of said cylinder member.
 3. A suspensionapparatus for a vehicle for permitting displacement of wheel supportmeans relative to a frame of said vehicle and for damping saiddisplacement, said apparatus comprising a hydraulic cylinder and pistonassembly, including:an elongated cylinder member defining a wallenclosed longitudinal bore and opposed head portions; a pistonreciprocably disposed for relative bidirectional movement in said boreand dividing said bore into opposed fluid chambers, and a piston rodconnected at one end to said piston and extending through one of saidchambers and one of said head portions to form a rod end chamber and asecond end chamber; piston rod seal means supported by said cylindermember and including means in fluid sealing engagement with said pistonrod to prevent leakage of fluid from said one chamber to the exterior ofsaid apparatus; a compressible liquid fluid filling the chambers; meansfor interconnecting said apparatus between said frame and said wheelsupport means whereby said piston and piston rod are forced into thecylinder until the fluid is compressed sufficiently in said cylindermember to support the vehicle while permitting displacement of saidwheel support means; flow restriction means for permitting onlyrestricted flow of fluid from one chamber to the other chamber inresponse to reciprocation of said piston and piston rod with respect tosaid cylinder member to provide for damped displacement of said wheelsupport means; means attached to the piston and piston rod for at leastretarding the intermingling of the fluid after the fluid has passedthrough the restrictive flow means and been heated therein with themajor portion of the fluid in the second end chamber while maintainingthe heated fluid in heat exchange relationship with the piston member,piston rod and cylinder wall adjacent thereto, said means formaintaining said heat exchange relationship including passage meansdefined at least in part by said piston for directing the flow of fluidalong the borewall of said cylinder member during movement of saidpiston to displace fluid from one of said chambers toward the other ofsaid chambers, and hydraulic cushion means for arresting the movement ofsaid piston as it approaches contact with said one head portion, saidcushion means including one of said chambers and a cavity formed byfirst annular means on said piston rod engageable with a second annularmeans on said one head portion to form a cavity which upon engagement ofsaid first annular means with said second annular means is hydrualicallyseparated from said one of said chambers to an extent sufficient toestablish a lower pressure in said cavity than in said chamber, saidcavity being in sufficiently high dynamic fluid communication with saidpiston rod seal means and with the other of said chambers to preventdynamic high fluid pressure peaks in said chamber from acting on saidpiston rod seal means.
 4. The apparatus set forth in claim 3wherein:said hub means includes means for providing greater restrictionto flow of fluid in said one direction, said greater restriction to flowof fluid being provided by said passage means in said hub means inseries flow communication with passage means in said piston duringmovement of said piston rod from said cylinder.
 5. The apparatus setforth in claim 4 including:passage means in said valve member operableto communicate with said passage means in said piston to providecontrolled displacement of fluid from said one chamber to cushion theextension of said piston rod when said hub means enters into engagementwith said ring seal.
 6. The apparatus set forth in claim 3 including:ametallic elongated cylindrical sleeve extending in sleeved relationshipover said cylinder member and having a head at one end connected to saidpiston rod in heat exchange relationship and forming between said headand said one head portion of said cylinder a pumping chamber open toatmosphere around said cylinder member, the extension and retraction ofsaid piston rod with respect to said cylinder member causing ambient airto be pumped into and out of said pumping chamber, respectively, totransfer heat away from said cylinder member and said piston rod throughsaid cylindrical sleeve.
 7. The apparatus set forth in claim 3including:resilient pad means secured intervening between said head andsaid one head portion of said cylinder to cushion the retraction of saidpiston rod at its retracted limit position.
 8. A suspension apparatusfor a vehicle for permitting displacement of wheel support meansrelative to a frame of said vehicle and for damping said displacement,said apparatus comprisinga hydraulic cylinder filled with a compressibleliquid under pressure and piston assembly including: an elongatedcylinder member including a longitudinal bore and opposed heat portions;a piston reciprocably disposed in said bore and dividing said bore intoopposed fluid chambers, and a piston rod connected at one end to saidpiston and extending through one of said chambers and one of said headportions; piston rod seal means supported by said cylinder member andincluding means in fluid sealing engagement with said piston rod toprevent leakage of fluid from said one chamber to the exterior of saidapparatus; means for interconnecting said apparatus between said frameand said wheel support means whereby said piston and piston rod areextended and retracted in said cylinder member to provide for dampeddisplacement of said wheel support means; and means formed by the pistonfor causing restricted flow of fluid from one chamber to the otherchamber in response to reciprocation of said piston and piston rod withrespect to said cylinder member and a valve member slidably disposed onsaid piston rod between the piston and the seal means, said valve memberincluding passage means formed thereby arranged to be in series flowcommunication with passage means in said piston as the piston movestoward the seal means to provide additional resistance to fluid flowbetween said chambers when the piston moves toward the seal means thanin the other direction of movement of said piston, the valve memberbeing shiftable by differential pressures produced by flow of the liquidpast the piston during stroking of the piston.
 9. The apparatus setforth in claim 8 wherein:said valve member is movable relative to saidpiston in the other direction of movement of said piston to provide forcommunicating said passage means in said piston directly with said onechamber, and said valve member includes a radially extending flangeportion cooperable with said piston to form passage means for directingthe flow of fluid radially outwardly toward the borewall of saidcylinder member.
 10. A suspension apparatus for a vehicle for permittingdisplacement of wheel support means relative to a frame of said vehicleand for damping said displacement, said apparatus comprising a hydrauliccylinder and piston assembly including:an elongated cylinder memberincluding a longitudinal bore and opposed heat portions; a pistonreciprocably disposed in said bore and dividing said bore into opposedfluid chambers, and a piston rod connected at one end to said piston andextending through one of said chambers and one of said head portions;piston rod seal means supported by said cylinder member and includingmeans in fluid sealing engagement with said piston rod to preventleakage of fluid from said one chamber to the exterior of saidapparatus; means for interconnecting said apparatus between said frameand said wheel support means whereby said piston and piston rod areextended and retracted in said cylinder member to provide for dampeddisplacement of said wheel support means; means formed by the piston forcausing restricted flow of fluid from one chamber to the other chamberin response to reciprocation of said piston and piston rod with respectto said cylinder member and a valve member slidably disposed on saidpiston rod between the piston and the seal means, said valve memberincluding passage means formed thereby arranged to be in series flowcommunication with passage means in said piston as the piston movestoward the seal means to provide greater resistance to fluid flowbetween said chambers when the piston moves toward the seal mean than inthe other direction of movement of said piston; said valve member ismovable relative to said piston in the other direction of movement ofsaid piston to provide for communicating said passage means in saidpiston directly with said one chamber, and said valve member includes aradially extending flange portion cooperable with said piston to formpassage means for directing the flow of fluid radially outwardly towardthe borewall of said cylinder member; and hydraulic cushion means forarresting the movement of said piston as it approaches contact with saidone head portion, said cushion means including one of said chambers anda cavity formed by first annular means on said piston rod engageablewith a second annular means on said one head portion to form a cavitywhich upon engagement of said first annular means with said secondannular means is hydrualically separated from said one of said chambersto an extent sufficient to establish a lower pressure in said cavitythan in said chamber, said cavity being in sufficiently high dynamicfluid communication with said piston rod seal means and with the otherof said chambers to prevent dynamic high fluid pressure peaks in saidchamber from acting on said piston rod seal means.
 11. The apparatus setforth in claim 10 including:passage means in said valve means memberoperable to communicate with said passage means in said piston toprovide controlled displacement of fluid from said one chamber tocushion the extension of said piston rod when said sleeve member entersinto engagement with said ring seal.
 12. A vibration isolation anddamping apparatus particularly useful for a vehicle for permittingdisplacement of wheel support means relative to a frame of said vehicleand for damping said displacement, said apparatus comprising a hydrauliccylinder and piston assembly including:an elongated cylinder memberincluding a longitudinal bore and opposed head portions; a pistonreciprocably disposed in said bore and dividing said bore into opposedfirst and second fluid chambers, and a piston rod connected at one endto said piston and extending through said first chamber and one of saidhead portions, the volume of the second chamber being substantiallygreater than the volume of the first to provide a relatively compliantspring constant; a compressible liquid filling the first and secondfluid chambers and being compressed to establish a force tending toexpel the rod from the cylinder against a load; means for causingrestricted flow of fluid from one chamber to the other chamber inresponse to linear extension and retraction of said piston and pistonrod with respect to said cylinder; and means for causing a portion ofthe fluid flowing from one chamber to the other to be largely confinedin heat exchange relationship with the piston and the adjacent portionof the cylinder during normal, less extreme excursions of the piston toproduce a zone of substantially elevated temperature having a relativelysmall volume as compared to the temperature of the significantlyrelatively larger volume of the second chamber to minimize heating ofthe bulk of the fluid disposed in said second chamber, whereby acompliant spring force with a relatively high damping ratio in the rangeof approximately 0.04 to 0.6 can be achieved without materially changingthe ride height due to an increase in pressure caused by temperatureincrease of the liquid.
 13. A suspension apparatus for a vehicle forpermitting displacement of wheel support means relative to a frame ofsaid vehicle and for damping said displacement, said apparatuscomprising a hydraulic cylinder and piston assembly including:anelongated cylinder member including a longitudinal bore defined by aborewall and opposed head portions; a piston reciprocably disposed insaid bore and dividing said bore into opposed fluid chambers and apiston rod connected at one end to said piston and extending through oneof said chambers and one of said head portions; piston rod seal meanssupported by said cylinder member and including means in fluid sealingengagement with said piston rod to prevent leakage of fluid from saidone chamber to the exterior of said apparatus; means for causingrestricted flow of fluid from one chamber to the other chamber inresponse to linear extension and retraction of said piston and pistonrod with respect to said cylinder member; means for interconnecting saidapparatus between said frame and said wheel support means whereby saidpiston and piston rod are extended and retracted in said cylinder memberto provide for damped displacement of said wheel support means; passagemeans defined at least in part by said piston for causing fluid flowingbetween said chambers to be directed along said borewall into heatexchange contact with said cylinder member to provide for heat transferaway from said fluid to minimize heating of fluid disposed in saidcylinder member; and hydraulic cushion means for arresting the movementof said piston toward said one head portion, said cushion meansincluding one of said chambers and cylindrical hub means on said pistonrod engageable with a ring seal on said one head portion to form acavity upon engagement of said hub means with said ring seal, saidcavity being in communication with the other of said chambers throughsaid passage means defined by said piston and through passage meansformed in said hub means to prevent high fluid pressure from acting onsaid piston rod seal means.
 14. A suspension apparatus for a vehicle forpermitting displacement of wheel support means relative to a frame ofsaid vehicle and for damping said displacement, said apparatuscomprising a hydraulic cylinder and piston assembly including:anelongated cylinder member including a longitudinal bore and opposed headportions; a piston reciprocably disposed in said bore and dividing saidbore into opposed fluid chambers and a piston rod connected at one endto said piston and extending through one of said chambers and one ofsaid head portions; piston rod seal means supported by said cylindermember and including means in fluid sealing engagement with said pistonrod to prevent leakage of fluid from said one chamber to the exterior ofsaid apparatus; means for causing restricted flow of fluid from onechamber to the other chamber in response to linear extension andretraction of said piston and piston rod with respect to said cylindermember; means for interconnecting said apparatus between said frame andsaid wheel support means whereby said piston and piston rod are extendedand retracted in said cylinder member to provide for damped displacementof said wheel support means; means for causing fluid flowing betweensaid chambers to be directed along said borewall into heat exchangecontact with said cylinder member to provide for heat transfer away fromsaid fluid to minimize heating of fluid disposed in said cylindermember; and hydraulic cushion means for arresting the movement of saidpiston toward said one head portion, said cushion means including one ofsaid chambers and cylindrical hub means on said piston rod engagementwith seal means on said one head portion to form a cavity being incommunication with passage means formed in said hub means and openinginto the other of said chambers to prevent high fluid pressure fromacting on said piston rod seal means.
 15. A suspension apparatus for avehicle for permitting displacement of wheel support means relative to aframe of said vehicle and for damping said displacement, said apparatuscomprising a hydraulic cylinder and piston assembly including:anelongated cylinder member including a longitudinal bore and opposed headportions; a piston reciprocably disposed in said bore and dividing saidbore into opposed fluid chambers, and a piston rod connected at one endto said piston and extending through one of said chambers and one ofsaid head portions; piston rod seal means supported by said cylindermember and including means in fluid sealing engagement with said pistonrod to prevent leakage of fluid from said one chamber to the exterior ofsaid apparatus; means for interconnecting said apparatus between saidframe and said wheel support means whereby said piston and piston rodare extended and retracted in said cylinder member to provide for dampeddisplacement of said wheel support means; means for causing restrictedflow of fluid from one chamber to the other chamber in response tolinear extension and retraction of said piston and piston rod withrespect to said cylinder member including a valve member slidablydisposed on said piston rod between said piston and said one headportion, said valve member including passage means formed therein andarranged to be in series flow communication with passage means in saidpiston in one direction of movement of said piston to provide greaterresistance to fluid flow between said chambers than in the otherdirection of movement of said piston; and hydraulic cushion means forarresting the movement of said piston toward said one head portion, saidcushion means including a hub portion of said valve member engageablewith seal means on said one head portion to form a cavity uponengagement of said hub portion with said seal means on said one headportion, said cavity being in communication with said passage means insaid piston through passage means formed in said hub portion to preventhigh fluid pressure from acting on said piston rod seal means.
 16. Theapparatus set forth in claim 15 including;passage means in said valvemember operable to communicate with said passage means in said piston toprovide controlled displacement of fluid from said one chamber tocushion the extension of said piston rod when said valve member entersinto engagement with said seal means on said one head portion.
 17. Asuspension apparatus for a vehicle for permitting bounce and rebounddisplacement of wheel support means relative to a frame of said vehicleand for damping said displacement, said apparatus comprising:anelongated cylinder member including a longitudinal bore and first andsecond opposite end closure means; piston means reciprocably disposed insaid bore and dividing said bore into first and second chambers, saidchambers each being filled with a confined compressible liquid; pistonrod means coupled to said piston and extending through at least thefirst end closure means, the piston rod means having a greater diameterin said first chamber than in said second chamber whereby as the pistonis moved toward the second chamber the liquid is compressed; piston rodseal means supported by at least one of the end closures and in fluidsealing engagement with the piston rod to prevent leakage of fluid fromthe chambers to the exterior of said apparatus; means forinterconnecting said apparatus between said frame and said wheel supportmeans whereby said piston and piston rod are extended and retracted insaid cylinder member to provide for bound and rebound displacement ofsaid wheel support means whereby displacement of the rod as it isstroked from the first chamber of the cylinder by the weight of thevehicle toward the second chamber will compress the liquid to provide areactive spring force supporting the vehicle while permittingreciprocating movement of the wheel relative to the vehicle body as thevehicle traverses uneven terrain; and the total volume of liquid in thesecond chamber being substantially greater than that in the firstchamber to provide a desired spring rate; damping means for providingcontrolled flow of fluid between the chambers in response toreciprocation of the piston means within the cylinder, said dampingmeans comprising fluid passageway means formed by the piston meansproviding resistance to fluid flow from the second end chamber to thefirst end chamber of a first magnitude sufficient to produce a firstdamping force during the bounce stroke and a second resistance to fluidflow from the first end chamber to the second end chamber greater thanthe first resistance and sufficient to produce a second damping forceduring the rebound stroke significantly greater in magnitude than thefirst damping force, a portion of the second pressure drop being causedby liquid passageways for restricting the flow of the liquidtherethrough spaced from the point at which the liquid passing throughthe piston mingles with the liquid in the second chamber, the liquidpassageways including a zone of decreased cross sectional area forproducing a pressure drop followed by a zone of substantially increasedcross sectional area and volume to increase retention time followed by azone of decreased cross sectional area to limit intermingling betweenthe increased volume zone and fluid in the second chamber, whereby theliquid heated by friction during bounce will be largely confined in thepassageways and first end chamber during normal operation and betransferred to the structure forming the passageways before intermixingwith the major portion of the liquid in the second chamber during asubstantial rebound stroke.
 18. The suspension apparatus of claim 17wherein the damping means comprises:a piston member fixed to the rodmeans for movement therewith having fluid passageways therethrough forproviding the first damping force on the bounce stroke; and meansmovable axially of the piston rod means and disposed between the pistonmember and the first chamber and movable toward the piston member inresponse to the rebound stroke for increasing the resistance to flow ofliquid from the first chamber by the piston member to the second chamberto produce the second damping force during the rebound stroke.
 19. Asuspension for a vehicle for permitting displacement of wheel supportmeans relative to a frame of said vehicle and for damping saiddisplacement, said apparatus comprising a hydraulic cylinder and pistonassembly including:an elongated cylinder member including a longitudinalbore and opposed head portions; a piston reciprocably disposed in saidbore and dividing said bore into opposed fluid chambers, and a pistonrod connected at one end to said piston and extending through one ofsaid chambers and one of said head portions; piston rod seal meanssupported by said cylinder member and including means in fluid sealingengagement with said piston rod to prevent leakage of fluid from saidone chamber to the exterior of said apparatus; means for interconnectingsaid apparatus between said frame and said wheel support means wherebysaid piston and piston rod are extended and retracted in said cylindermember within a normal range generally centered about the normal rideheight to provide for damped displacement of said wheel support means;and means for causing restricted flow of fluid from one chamber to theother chamber in response to reciprocation of said piston and piston rodwith respect to said cylinder member within the normal ranges includinga first set of fluid passageways through the piston and a valve memberslidably disposed on said piston rod between the piston and the pistonrod seal means, said valve member including passage means formed therebyand arranged to be in series flow communication with passage means insaid piston during movement of said piston toward the piston rod sealmeans to provide greater resistance to fluid flow between said chamberswhen the piston is moving toward the rod seal means than in the otherdirection of movement of said piston.
 20. A suspension apparatus for avehicle for permitting displacemnt of wheel support means relative to aframe of said vehicle and for damping said displacement, said apparatuscomprising a hydraulic cylinder and piston assembly including:anelongated cylinder member including a longitudinal bore and opposed headportions; a piston means reciprocably disposed in said bore and dividingsaid bore into opposed first and second fluid chambers, and a piston rodconnected at one end to said piston and extending through the firstchamber and one of said head portions; a compressible liquid filling thefirst and second chambers; piston rod seal means supported by saidcylinder member and including means in fluid sealing engagement withsaid piston rod to prevent leakage of fluid from the first chamber tothe exterior of said apparatus; the piston means including means forpermitting restricted flow of fluid between the chambers in response toreciprocation of said piston and piston rod with respect to saidcylinder member; means for interconnecting said apparatus between saidframe and said wheel support means whereby said piston and piston rodare forced into the cylinder to provide a reaction spring force forsupporting the vehicle while providing for displacement of said wheelsupport means; means associated with the piston for reducing mixing ofthe heated fluid flowing through the means for causing restricted flowof fluid during normal reciprocation of the piston with the majorportion of the liquid in the second chamber including means travelingwith the piston forming a zone of relatively increased volume and lowvelocity between a high velocity zone causing pressure drop and dampingand a restricted opening communicating with the second chamber wherebythe liquid in the vicinity of the piston, rod and adjacent cylinder willbe primarily heated and the heat transferred away from the fluid throughsaid members with minimum change of volume of the liquid due to heatgenerated by the flow restricting means during operation to reducechange in normal average position of the piston during operation. 21.The suspension apparatus of claim 20 wherein the means for reducingmixing of the heated fluid from the remainder of the fluid in the secondchamber includes baffle means connected to the piston and spacedtherefrom to define a subchamber movable with the piston, the subchamberbeing in fluid communication with the fluid in the remainder of thechamber through restricted opening means.
 22. A suspension apparatus fora vehicle for permitting displacement of wheel support means relative toa frame of said vehicle and for damping said displacement, saidapparatus comprising:an elongated cylinder member including alongitudinal bore and a rod end closure and a second end closure; pistonmeans reciprocably disposed in said bore and dividing said bore into arod end chamber adjacent the rod end closure and a second end chamberadjacent the second end closure, said chambers being filled with aconfined compressible liquid, a piston rod connected at one end to saidpiston means and extending through the rod end closure; piston rod sealmeans supported by the rod end closure and in fluid sealing engagementwith the piston rod to prevent leakage of fluid from the rod end chamberto the exterior of said apparatus; means for interconnecting saidapparatus between said frame and said wheel support means whereby saidpiston and piston rod are extended and retracted in said cylinder memberto provide for displacement of said wheel support means wherebydisplacement of the rod as it is stroked into the cylinder by the weightof the vehicle will compress the liquid to provide a reactive springforce supporting the vehicle while permitting reciprocating movement ofthe wheel relative to the vehicle body as the vehicle transverses uneventerrain; and means forming a resilient liquid cushion for reducing theimpact of the piston means against the rod end closure upon unloadedextension of the apparatus including means on the piston means acting incooperation with means on the rod end closure to confine a limitedvolume of the liquid to produce an increased pressure acting to retardthe progress of the piston means toward the end closure means includingmeans for venting the pressure of the liquid acting on the piston rodseal means to the liquid on the other side of the piston means to reducethe peak pressure acting on the seal means as compared to the pressureof the liquid cushion.
 23. A system for producing a spring force underload conditions comprising:hydraulic cylinder means having at least onerod end, rod means extending through the rod end having a seal portionof constant diameter for reciprocation through the rod end and formingpiston means within the cylinder having a larger diameter than the sealportion and dividing the cylinder means into a first chamber around theseal portion and a second chamber on the opposite side of the pistonmeans, seal means forming an annular, sliding fluid seal between thecylinder and the seal portion of the end, a compressible liquid underpressure within the cylinder for producing a spring force tending toforce the rod means out of the cylinder means to thereby counteract aload tending to force the rod means into the cylinder means, the rodmeans and piston cooperating with the cylinder means to form a zone ofprogressively increasing pressure as the piston approaches the rod endof the cylnder means at velocity resulting from a decreased loadcondition for progressively increasing the rate of deceleration of thepiston means before impact with the cylinder means, and fluid controlmeans associated with the rod means and cylinder means for preventingpressure acting on the seal means from increasing at the same rate asthe pressure acting to decelerate the piston means after the rod meanshas reached a predetemrined position of travel relative to the rod endto thereby limit the pressure acting on the seal while maintaining thehigher pressure acting to prevent travel of the rod means to preventdamaging mechanical contact between the piston and cylinder in responseto a sudden reduced load condition.
 24. The system of claim 23 whereinthe fluid control means comprisesmeans for establishing, at thepredetermined position of travel, high and low pressure zones betweenthe piston and rod end, the high pressure zone acting on an area of thepiston and a generally corresponding area of the rod end of thecylinder, the low pressure zone acting on an area of the piston and theseal means, and port means for passing fluid from the low pressure zonepast the piston to the second chamber, such that the buildup of pressurein the high pressure zone is at a greater rate than the buildup ofpressure in the low pressure zone.
 25. The system of claim 23 whereinthe fluid control means comprisesmeans for establishing, at thepredetermined position of travel, high and low pressure zones betweenthe piston and rod end, the high pressure zone acting on an area of thepiston and a generally corresponding area of the rod end of thecylinder, the low pressure zone acting on an area of the piston and theseal means, first port means for passing fluid from the high pressurezone past the piston to the second chamber, second port means forpassing fluid from the low pressure zone past the piston to the secondchamber, the first and second port means being sized relative to thevolumes of the high and low pressure zones such that the buildup ofpressure in the high pressure zone is at a greater rate than the buildupof pressure in the low pressure zone.
 26. A suspension apparatus for avehicle for permitting displacement of wheel support means relative to aframe of said vehicle and for damping said displacement, said apparatuscomprising a hydraulic cylinder and piston assembly, including:anelongated cylinder member defining a wall enclosed longitudinal bore andopposed head portion; a piston reciprocably disposed for relativebidirectional movement in said bore and dividing said bore into opposedfluid chambers, and a piston rod connected at one end to said piston andextending through one of said chambers and one of said head portions toform a rod end chamber and a second end chamber; piston rod seal meanssupported by said cylinder member and including means in fluid sealingengagement with said piston rod to prevent leakage of fluid from saidone chamber to the exterior of said apparatus; a compressible liquidfluid filling the chambers; means for interconnecting said apparatusbetween said frame and said wheel support means whereby said piston andpiston rod are forced into the cylinder until the fluid is compressedsufficiently in said cylinder member to support the vehicle whilepermitting displacement of said wheel support means; hydraulic cushionmeans for arresting the movement of said piston as it approaches contactwith said one head portion, said cushion means including one of saidchambers and a cavity formed by first annular means on said piston rodengageable with a second annular means on said one head portion to forma cavity which upon engagement of said first annular means with saidsecond annular means is hydrualically separated from said one of saidchambers to an extent sufficient to establish a lower pressure in saidcavity than in said chamber, said cavity being in sufficiently highdynamic fluid communication with said piston rod seal means and with theother of said chambers to prevent dynamic high fluid pressure peaks insaid chamber from acting on said piston rod seal means.
 27. Theapparatus set forth in claim 26 wherein:said hub means includes a valvemember for providing greater restriction to flow of fluid in said onedirection, said greater restriction to flow of fluid being provided bysaid passage means in said hub means in series flow communication withpassage means in said piston during movement of said piston rod fromsaid cylinder.
 28. The apparatus set forth in claim 27 including:passagemeans in said valve member operable to communicate with said passagemeans in said piston to provide controlled displacement of fluid fromsaid one chamber to cushion the extension of said piston rod when saidhub means enters into engagement with said ring seal.